This invention relates to novel compositions of matter containing optically pure (xe2x88x92) amlodipine. These compositions possess potent activity in treating both systolic and diastolic hypertension while avoiding adverse effects including but not limited to edema of the extremities, headache and dizziness, which are associated with administration of the racemic mixture of amlodipine. Additionally, these novel compositions of matter containing optically pure (xe2x88x92) amlodipine are useful in treating angina and such other conditions as may be related to the activity of (xe2x88x92) amlodipine as a calcium channel antagonist including but not limited to cerebral ischemia, cerebral disorders, arrhythmias, cardiac hypertrophy, coronary vasospasm, myocardial infarction, renal impairment and acute renal failure xe2x80x94xe2x80x94while avoiding the adverse effects associated with administration of the racemic mixture of amlodipine. Also disclosed are methods for treating the above-described conditions in a human while avoiding the adverse effects that are associated with the racemic mixture of amlodipine, by administering the (xe2x88x92) isomer of amlodipine to said human.
Many organic compounds exist in optically active forms, i.e., they have the ability to rotate the plane of plane-polarized light. In describing an optically active compound, the prefixes D and L or R and S are used to denote the absolute configuration of the molecule about its chiral center(s). The prefixes d and l or (+) and (xe2x88x92) are employed to designate the sign of rotation of plane-polarized light by the compound, with (xe2x88x92) or 1 meaning that the compound is levorotatory. A compound prefixed with (+) or d is dextrorotatory. For a given chemical structure, these compounds, called stereoisomers, are identical except that they are mirror images of one another. A specific stereoisomer may also be referred to as an enantiomer, and a mixture of such isomers is often called an enantiomeric or racemic mixture.
Stereochemical purity is of importance in the field of pharmaceuticals, where 12 of the 20 most prescribed drugs exhibit chirality. A case in point is provided by the L-form of the xcex2-adrenergic blocking agent, propranolol, which is known to be 100 times more potent than the D-enantiomer.
Furthermore, optical purity is important since certain isomers may actually be deleterious rather than simply inert. For example, it has been suggested that the D-enantiomer of thalidomide was a safe and effective sedative when prescribed for the control of morning sickness during pregnancy, while the corresponding L-enantiomer has been thought to be a potent teratogen.
The active compound of this composition and method is an optical isomer of the compound amlodipine, which is described in Campbell et al., U.S. Pat. No. 4,572,909. Chemically, this (xe2x88x92) isomer is 3-ethyl 5-methyl (xe2x88x92)-2-[(2-aminoethoxy) methyl]-4-(2-chlorophenyl)-1,4-dihydro-6-methyl-3,5-pyridine-dicarboxylate. This isomer will hereinafter be referred to as (xe2x88x92) amlodipine. (xe2x88x92) amlodipine also includes the substantially optically pure (xe2x88x92) amlodipine isomer.
Amlodipine, which is the subject of the present invention, is available commercially only as the 1:1 racemic mixture. That is, it is available only as the 1:1 mixture of optical isomers, called enantiomers. The racemic mixture of amlodipine that is commercially available for administration is a besylate salt.
The racemic mixture of amlodipine is in the class of compounds known as calcium antagonists. The concept of a specific mechanism of pharmacologic action related to the antagonism of calcium movement in the process of excitation-contraction was suggested by Fleckenstein et. al. (see Fleckenstein, A., Calcium Antagonism in Heart and Smooth Muscle:Experimental Facts and Therapeutic Prospects, New York, Wiley, 1983; Swamy, V. and D. Triggle, Modern Pharmacology, 2nd. Ed., Craig and Stitzel, Eds., Little, Brown and Co., Boston, 1986, Chapt. 26, 373-380; Triggle, D. J., and R. A. Janis, Ann. Rev. Pharm. and Tox. 27: 347-369, 1987). Many of the currently available calcium antagonists appear to antagonize the entry of calcium through voltage dependent channels in the plasma membrane of cells. The pharmacologic class of calcium antagonists consists of chemically diverse compounds. Given the structural heterogeneity of the class it is likely that the pharmacological action involves more than one site or mechanism of action.
Amlodipine is one of a series of dihydropyridine calcium antagonists. However, amlodipine has a generally slower onset and longer duration of action than, for example, nifedipine. (Jensen, H. et al., J. Hum. Hypertens., 42(5): 541-45, 1990). The metabolites of amlodipine apparently do not possess significant calcium channel blocking activity, while the parent drug offers a biological half-life of some 35-40 hours, prompting a once-daily dosage regimen. (Lorimer, A. R., et al., J. Hum. Hypertens., 3(3): 191-96, 1989; Glasser, S. F. et al., AJH, 2(3): 154-57, 1989). Its ability to block, calcium channels in smooth muscle produces peripheral vasodilation resulting in decreases in both systolic and diastolic blood pressure.
With regard to the enantiomers of amlodipine, these are disclosed in Arrowsmith et al. J. Med. Chem., 29: 1696-1702 (1986). This reference discusses in vitro tests to determine calcium antagonist activity against calcium-induced constriction of potassium-depolarized rat aorta. The authors allege that in vitro evaluation of the enantiomers of amlodipine shows the (xe2x88x92) isomer to be twice as active as the racemic mixture in antagonizing calcium-induced constriction of potassium-depolarized rat aorta. The authors also allege that the (+) isomer of amlodipine is some 1,000 times less active in these in vitro tests. Further, European Patent Application No. 0 331 315 discloses a method for separation of the R(xe2x88x92) and S(+) isomers of amlodipine. While these references discuss the enantiomers of amlodipine, they only provide a method of synthesis and in vitro test results of the individual enantiomer activity as found in rat aorta. There is no disclosure of the effects of or a suggestion for administering one of the enantiomers of amlodipine to a human. Moreover, there is no disclosure or suggestion of the alleviation or reduction of side effects which is achieved by the administration of (xe2x88x92) amlodipine.
The racemic mixture of amlodipine is presently used primarily as an antihypertensive agent; it is generally taken orally as a once-daily therapy. As stated above, the racemic mixture of amlodipine produces peripheral vasodilation, resulting in decreases in both systolic and diastolic blood pressure when used as an antihypertensive agent. This antihypertensive effect occurs in the relative absence of significant or sustained effects on cardiac rate.
While yet the subject of extensive research, hypertension appears to be the product of an inherited predispositionxe2x80x94coupled with dietary, emotional, and environmental factors, which results in a structural adaptation of the cardiac muscle and the large blood vessels. Most patients display heightened vascular and cardiac reactions to sympathetic nervous stimulation, but the precise relationship of sympathetic nervous stimulation to the etiology of the disease. Nevertheless, hypertension results in chronic readjustment of cardiovascular hemodynamics, alteration of blood vessel walls, cardiovascular resistance and regional transmural pressures.
Pharmacologic management of hypertension is generally directed to the normalization of altered hemodynamic parameters, and many drugs and drug classes, either as monotherapy or in combination treatment, can reduce and control elevated blood pressure. However, treatment of hypertension does not always correspondingly benefit the morbidity and mortality of the condition, either because chronic hypertension has produced other significant and irreversible cardiovascular changes, or because present drugs have an adverse effect on some other risk factor for cardiovascular disease. Rather, current drug therapy simply provides sustained arterial pressure reduction.
Furthermore, the racemic mixture of amlodipine is useful in treating other disorders such as angina pectoris.
Angina pectoris is a highly variable, rather poorly understood clinical syndrome reflecting a myocardial ischemia. When cardiac work or myocardial oxygen demand exceeds the ability of the coronary arterial vascular system to supply oxygen, the resulting ischemia stimulates the sensory nerves of the heart, producing the sensation of angina characterized by episodes of precordial pressure, discomfort, or a severe, intense crushing pain which may radiate to several sites including the left shoulder and left arm. Physical activity or exertion characteristically initiates the condition, and rest or drug therapy relieves the condition. The signs and symptoms of an episode persist for a few minutes, but can be induced or exaggerated by a meal or exposure to cold air. Treatment is directed to the underlying disease, usually atherosclerosis, or to drugs which either reduce myocardial oxygen demand or improve oxygen supply. Calcium antagonists such as amlodipine have been particularly useful in treating vasospastic angina, the angina of effort, and the unstable angina, due to the effect of the calcium channel antagonist on cardiac and vascular smooth muscle.
Amlodipine may be useful in the treatment of cerebral ischemia. Cerebral ischemia, often the result of atherosclerotic disease or hypertension, results from insufficient cerebral circulation. Under normal circumstances, an extensive collateral circulation ensures adequate blood flow. However, cerebral ischemia may result from either an intra- or extracranial interruption of arterial blood flow. If interruption is transient, the cerebral tissues recover, and neurologic symptoms disappear. If the ischemia lasts for a somewhat more extended period, infarction results and the resulting neurologic damage is permanent. In the case of extended ischemia. resulting in infarction, treatment is directed to the underlying vascular disease, to blood platelet aggregation inhibitors, and anticoagulant therapy.
Because of its activity as a calcium channel antagonist, amlodipine may also be useful in treating cardiac arrhythmias. Cardiac arrhythmias represent a broad, complex group of electrophysiologic disorders that affect the mechanical properties of the heart and vasculature, altering normal cardiac rhythm, function and output. Normal cardiac rhythm originates with the sinoatrial node, which possesses high intrinsic automaticity. Adequate automaticity and conduction lead to activation of atrial and ventricular fibers, producing in sequence the elements of normal functional heart beat. Calcium antagonists may be of value in conditions where calcium-related changes in membrane potential and conduction alter normal rhythm. In the absence of treatment, symptoms vary with individual arrhythmias, but are often the consequence of inadequate cardiac filling and output and often include fatigue, decreased exercise tolerance, syncope, shortness of breath, nausea, lightheadedness and the like.
Amlodipine may be useful to treat cardiac hypertrophy. Cardiac hypertrophy can result from excessive workload either due to an obstruction to outflow, termed systolic overload, or to excessive volumes presented to the heart in diastole, termed diastolic overload. Systolic overload results in concentric ventricular hypertrophy, in which there is an increased thickness in the walls of the heart not associated with increased volume. Diastolic overload causes dilation and hypertrophy with an increased blood volume. An inadequate cardiac output results from the heart""s failure in systolic or diastolic overload, leading to fatigue, shortness of breath, pulmonary congestion, edema and the like. Calcium channel antagonists effect workload and, as such, may be useful in treating cardiac hypertrophy due to the effect of the calcium antagonist on cardiac and vascular smooth muscle in reducing blood pressure.
It is also possible that amlodipine could be used to treat coronary arterial spasm. Coronary arterial spasm can occur in the absence of significant coronary atherosclerosis and is thought to be an initiating event in variant angina and in myocardial infarction. Coronary spasm may occur without the patient feeling any significant discomfort. In an electrically unstable heart, diverse neural impulses to the heart may provoke coronary vascular spasm. This may result in enhanced myocardial ischemia and arrhythmia, which in turn may culminate in ventricular fibrillation and sudden cardiac death. As in variant or vasospastic angina, the calcium channel antagonists may be of particular usefulness due to their effect on cardiac and vascular smooth muscle.
Furthermore, amlodipine may be useful in the treatment of myocardial infarction, ischemic myocardial necrosis, and ischemia reperfusion injury. Myocardial infarction or ischemic myocardial necrosis generally results from the abrupt reduction of coronary blood flow to a portion of the myocardium The condition likely originates from atherosclerosis of the coronary arteries. Either coronary artery vasospasm or acute coronary thrombosis precipitates the condition, although the etiology is the subject of continuing research. Myocardial infarction is predominantly a disease of the left ventricle. Precordial pain and left ventricular dysfunction characterize the disease. The pain, which can be severe aching or pressure, leads to apprehension. Symptoms include left ventricular heart failure, pulmonary edema, shock or significant cardiac arrhythmia. Calcium channel antagonists may find utility in the management of myocardial infarction patients due to their effects on coronary artery vasospasm, blood pressure or other effects on cardiac function or vascular smooth muscle.
Amlodipine may be used to treat congestive heart failure. Congestive heart failure can be caused by hypertension, cardiomyopathy, coronary artery disease or valvular heart disease. Congestive failure results in poor cardiac output and elevated left-ventricular diastolic pressure, leading to dyspnea, fatigue, peripheral edema, and coughing. The ability of some calcium antagonists to lower afterload by dilating peripheral arteries without having a significant inotropic effect may increase their use in treating congestive heart failure.
Amlodipine may be of use in treating migraine. Classic migraine typically begins with visual auras followed by severe headaches, often accompanied by nausea and vomiting. Common migraine has similar symptoms without the preceding visual aura. The causes of migraine have been studied intensely, and are still a matter of debate. The most generally accepted cause is hypoxia due to reduced cerebral blood flow. Calcium channel antagonists have been used for migraine prophylaxis since they can increase cerebral blood flow.
Amlodipine may also be useful for treating Raynaud""s phenomenon, which is characterized by vascular spasm of the extremities. These vasospasms can be caused by cold or stress. A pallor or cyanosis is usually present due to severe constriction of the digital arteries. The phenomenon is often seen as a secondary disorder with arterial diseases or connective tissue diseases such as scleroderma, arthritis or lupus erythematosus. Calcium channel antagonists have been shown to be effective in treating Raynaud""s phenomenon.
Amlodipine may be useful in the treatment of asthma and bronchospasm. Symptoms of asthmaxe2x80x94coughing, wheezing, and dyspneaxe2x80x94are caused by constriction of tracheobronchial smooth muscle. Asthma attacks can be triggered by antigenic stimuli (pollen, dust) or non-antigenic stimuli (exercise, pollution, infection). The response to these stimuli lead to secretions of chemical mediators that cause smooth muscle contraction. Calcium channel antagonists can be used to control bronchoconstriction and relieve asthma attacks.
In addition, the racemic mixture of amlodipine may be useful to treat renal impairment and acute renal failure. Renal impairment and acute renal failure are clinical conditions of diverse etiology, which are associated with an increasing azotemia or urea nitrogen in the blood, and often an oliguria or a diminished volume of urine in relation to fluid intake. The pathophysiology may originate prerenally, manifest as inadequate renal perfusion, due to extracellular fluid volume depletion or cardiac failure. The most common cause of intrinsic renal failure is prolonged renal ischemia. Postrenal azotemia may be associated with obstruction or renal glomerular and tubular dysfunction. Laboratory findings disclose progressive azotemia, acidosis, hyperkalemia, and hyponatremia. Factors aggravating kidney impairment or failure must be specifically treated, including heart failure, obstruction and the like. Moderate or severe hypertension has a deleterious effect on renal function, and management of the hypertension with a variety of drugs including calcium channel antagonists may be useful therapy.
In addition, the racemic mixture of amlodipine could be useful in the treatment of cognitive disorders. Cognitive disorders include but are not limited to dementia and age-associated memory impairment.
Dementia can occur at any age. It is a structurally caused permanent or progressive decline in several dimensions of intellectual function that interferes substantially with individual normal social or economic activity.
One particular type of dementia is Alzheimers-type dementia. Alzheimers-type of dementia is thought to be due to a degenerative process, with a large loss of cells from the cerebral cortex and other brain areas. Acetylcholine-transmitting neurons and their target nerve cells are particularly affected. The brain shows marked atrophy with wide sulci and dilated ventricles. Senile plaques and neurofibrillary tangles are present. Memory loss is the most prominent early symptom. Disturbances of arousal do not occur early in the course. Alzheimer""s presenile and senile onset dementias are similar in both clinical and pathologic features, with the former commonly beginning in the 5th and 6th decades and the latter in the 7th and 8th decades. The dementia usually progresses steadily, becoming well advanced in 2 to 3 years. Some cases of dementia occurring in the presenile period are hard to classify and are sometimes labelled idiopathic or simple presenile dementia.
The signs and symptoms of dementia in particular Alzheimers-type dementia include depression, paranoia, anxiety or any of several other psychologic symptoms. The most common clinical picture is slow disintegration of personality and intellect due to impaired insight and judgment and loss of affect. Memory impairment increases, beginning with problems recalling recent events or finding names. The impairment varies greatly from time to time and often from moment to moment. Dementia generally is an insidious, slowly progressive, untreatable condition. However, the rate of progression varies widely and depends on the cause.
Another type of cognitive disorder is age-associated memory impairment (AAMI). AAMI is used to describe healthy non-demented people who have experienced memory loss over the course of the person""s life. Most commonly it is used to describe adults over the age of 50 who have experienced memory loss over the course of adult life. It has been estimated that between 25% and 50% of people over the age of 65 have this disorder.
Many calcium channel antagonists cause significant adverse effects. These adverse effects include but are not limited to tachycardia, orthostatic hypotension and fluid retention. In contrast to the situation with several other calcium channel antagonists, however, the racemic mixture of amlodipine has not been found to cause either marked or prolonged direct effects on heart rate or the reflex consequence of vasodilation.
However, the administration of the racemic mixture of amlodipine to a human has been found to cause still other adverse effects. These adverse effects include but are not limited to edema of, the extremities including peripheral edema, headache, flushing/hot flashes, fatigue, vertigo, muscle cramps and dizziness.
Thus, it would be particularly desirable to find a compound with the advantages of the racemic mixture of amlodipine which would not have the aforementioned disadvantages of significant adverse side effects and which was useful for treatment of other conditions.
It has now been discovered that the optically pure (xe2x88x92) isomer of amlodipine is an effective antihypertensive agent for both systolic and diastolic hypertension, particularly in mild to moderate disease and angina, while avoiding adverse effects including but not limited to edema of the extremities, headache and dizziness, which are associated with the administration of the racemic mixture of amlodipine. It has also been discovered that these novel compositions of matter containing optically pure (xe2x88x92) amlodipine are useful in treating other conditions as may be related to the activity of (xe2x88x92) amlodipine as a calcium channel antagonist, including but not limited to cerebral ischemia, cerebral disorders, arrhythmias, cardiac hypertrophy, coronary vasospasm, myocardial infarction, renal impairment and acute renal failure while avoiding the above-described adverse effects associated with the administration of the racemic mixture of amlodipine. The present invention also includes methods for treating the above-described conditions in a human while avoiding the adverse effects that are associated with the racemic mixture of amlodipine by administering the (xe2x88x92) isomer of amlodipine to said human.